Illumination device and method for illuminating an object

ABSTRACT

An illumination arrangement for illuminating an object to be measured, destined in particular for a coordinate measuring system or a measuring microscope, includes several light sources ( 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 60, 62, 64, 66, 68 ) going out from a support ( 16, 70 ) having different incidence angles with respect to an optical axis ( 14 ) of an optic, by means of which the object can be measured or imaged. The light sources in the support are arranged in such a way, that their incidence angles (α, β, γ, δ, κ) intersect the optical axis ( 14 ) in divergent areas ( 48, 50, 52, 54, 56 ).

The invention concerns an illumination arrangement for illuminating anobject to be measured, destined in particular for a coordinate measuringdevice or a measuring microscope, comprising several light sourcesextending from a support and having different incidence angles withrespect to an optical axis of an optic with which the object can bemeasured or imaged. The invention also concerns a process forilluminating an object having several light sources with divergentincidence angles with respect to an optical axis of an optic, with whichthe object is measured or imaged.

When using optical and multisensor coordinate measuring devices as wellas measuring microscopes, it is necessary to illuminate the objects tobe measured by means of suitable illumination arrangements. In these,the usual types of illumination are transmitted light, bright fieldincident light and dark field incident light. By selecting between thedifferent illumination possibilities in dependence upon the shape of theobject to be measured is ensured an optimal illumination. Thus, in darkfield illumination, only the light that is diffracted in the objectcontributes to the imaging, whereby individual structures appear brighton a dark background. In bright field illumination, the light to beemitted reaches directly into the object as transmitted light orincident light. The objects appear thus, insofar as they are themselvesrich in contrast, dark or colored on a bright background.

Of particular importance is the configuration of the dark field incidentillumination. Herein are used systems in the form of, for example, glassfiber ring lights or ring-shaped arrangements of LEDs(light-transmitting diodes). To be able to displace the illuminationangle within an unchanged working plane, the glass fiber ring lights aredivided into several segments or, to achieve the same results, the LEDareas can be connected and disconnected segment by segment. Because ofthis, there exists the possibility of exposing the object to be measuredto different lighting or to change the direction of incidence of thelighting.

Also known are proposals in which the angle between the surface of theobject to be measured and the illumination incidence beam can beconfigured differently by means of a simultaneous lifting and loweringof an illumination source or spherical arrangement of severalillumination sources. It is disadvantageous of these measures thatcollision problems with the object to be measured can occur due to thenecessary mechanical displacement of the illumination system. Arelatively complicated mechanism becomes necessary or the entire workingdistance is unfavorably reduced.

From DE 39 06 555 A1 an incident light object illumination device withselectable light incidence angle and several individually switchablelight sources is known. At the same time, an illumination at differentselectable illumination angles is possible without a mechanicaldisplacement of the light sources or imaging elements, and at the sametime, an illumination at different selectable illumination angles. Forthis purpose, the light sources going out from a calotte-shaped support,which can be arranged concentrically around a tube of a microscope, canall be aligned with respect to an object plane, so that the imagingdistance is to be selected always equal. An arrangement for this purposeis also conceivable for coordinate measuring apparatuses.

In a programmable surface illuminator for video testing devicesaccording to DE 199 04 899 A1, LEDs aligned parallel to each other goout from a disk-shaped support whose beams fall on a parabolic mirror,by means of which the radiation can fall on the object to be measured atincidence angles within a range between 45° and 90°.

It is also known to arrange a Fresnel lens between light sources such aslight-emitting diodes and an object to be measured so as to illuminatean object to be measured at different incidence angles (DE 198 37 797A1).

Other arrangements for illuminating an object at divergent incidenceangles focused on a mutual working plane are disclosed in U.S. Pat. No.4,893,223 or DE 196 53 234 A1.

From DE 40 16 264 C2 is known a fiberoptic multi-point lamp with acylinder-shaped head for illuminating the working field of a microscope.

To adjust the illumination of a fiberoptic multi-point lamp to a desiredobject field, light conducting fiber bundles are configured so as to bemovable according to DE 32 00 938 A1.

It is an object of the invention to further develop an illuminationarrangement as well as a process for illuminating an object in such away that a problem-free adjustment of the illumination is possiblewithin different working planes so as to optimally illuminate an objectto be measured or a surface or edge of the object. A limitation of themeasuring range should at the same time not take place due to the lightsources themselves.

The object is attained according to the invention essentially by meansof an illumination arrangement of the kind described above by arrangingthe light sources in such a way within a support that their incidenceangles intersect the optical axis within areas, which are spaced withrespect to each other, in particular within divergent working distancesof the optic. It is provided especially that the light sources on theoptical axis are preferably arranged on concentrically surroundingcircles, while the light sources arranged on circles of differentdiameters can intersect the optical axis in areas having divergentworking distances.

The support for the light sources can span a plane that verticallyintersects the optical axis. The support can therein form a circulardisk or can also consist of only one or several cubic or beam-shapedholders for the light sources.

There is also the possibility of configuring the support in the shape ofa hood or calotte that in turn surrounds concentrically the opticalaxis.

To make possible a high density of the light sources to be mounted, theinvention provides that the light sources such as LEDs are arrangedradially offset with respect to each other on successive circles.

The support having the desired geometry should have recesses such asbores, in which the light sources can be preferably fixedly arranged.However, there is also the possibility of displacing as well as pivotingthe light sources themselves in the individual recesses.

It is especially provided that the support is in itself verticallyadjustable, that is, it is configured so as to be displaceable along theoptical axis. Such an arrangement is suitable in particular for ameasuring arrangement with an optic, which has a constant or essentiallyconstant working distance.

In a support with a calotte or hood-shaped geometry, the same shouldhave at its object side an area for accommodating the light sources witha radius of curvature of 40 mm≦R≦80 mm, in particular R of about 60 mm.Through this, the light sources can be arranged in such a way inparticular on circles running concentrically with respect to each other,that the beams intersect the working plane at an angle of 5° to up to,for example, 85°, without the support having to have a height thatcauses the danger of a collision with the object to be measured. At thesame time, it is not required that the support be displaced with respectto the optic or the housing wherein it is accommodated.

An angular adjustment between the illumination beam and the surface ofthe object can take place according to the invention by means ofdifferent angular positions of fixedly arranged light sources, whereinthese are arranged within a plane that is located in a collision-freespace. In dependence upon the effective working distance or area to beilluminated are used those light sources whose angular positions arealigned with respect to the working distance or operating range. Viceversa, the angular displacement is achieved by changing the effectiveworking distance of the used optic or the optical system. Of course,there is also the possibility of utilizing always all or essentially allof the light sources to illuminate the object, wherein always an optimalillumination of the object takes place on the working plane, since inaccordance with the invention groups of light sources intersect theoptical axis of the optic in different areas or sections. Consequently,in this case, the work can be carried out without additional mechanicaldisplacement at different illumination incidence angles as well as alsosufficiently long working distances.

If the illumination arrangement of the invention is destined inparticular for dark field incident light processes, then it is possibleto use the arrangement also for bright field incidence measurementswithout problems. For this purpose, it is provided that the radiationemitted by the light sources is deflected in such a way that these meetalong the optical axis on the object. Of course, the imaging optic canalso be provided in the usual way for a bright field incident lightarrangement.

If, as mentioned, the light sources are preferably LEDs, then also fiberbundles and/or fiber ring segments can be used to realize the teachingof the invention. As light sources are also suitable, however, mirrorsby means of which the light can be deflected in such a way that theincidence angles of the radiations reflected by the mirrors intersectthe optical axis of the optic in divergent areas, in particular workingdistances.

In a further development, it is provided that the optic comprisesseveral cameras provided at different distances between the lens vertexand the back focus, to which is assigned a mutual objective with fixedfocal distance. The optic can also comprise several objective-camerasystems, which have divergent working distances with respect to theobject.

Independently thereof, the optic can be configured as zoom optic with avariable working distance, that is, it can have a design as seen in WO99/53268, to whose disclosure is made reference expressly herein.

The light sources can also illuminate the object with divergent colors,wherein, if required, light sources with an identical incidence angleilluminate the object with the same color.

A process for illuminating an object with several light sources havingdivergent incidence angles with respect to an optical axis of an opticsmechanism, with which the object is measured or imaged, is characterizedin that the incidence angle of the light sources is aligned in such away with respect to the optical axis that different light sourcesintersect the optical axis in areas, which are spaced with respect toeach other. At the same time, the object can be illuminated with thelight sources whose incident angles are aligned in dependence upon theworking distance. There is also the possibility of adjusting the workingdistance of the optic in dependence upon the incidence angle of one ofthe light sources that illuminate an area of the object to be measured.

Finally, a support that accommodates the light sources can be displacedalong the optical axis with a fixed working distance of the optic so asto illuminates the object with desired incidence angle.

Further details, advantages, and features of the invention do not resultonly from the claims, the features disclosed therein, per se and/or incombination, but also from the following description of the preferredexemplary designs seen in the drawings.

In the drawings,

FIG. 1 shows a schematic diagram of an illumination arrangement of anoptical measuring device,

FIG. 2 shows in sectional view a support for the illuminationarrangement according to FIG. 1,

FIG. 3 shows an alternative design of the illumination arrangement ofFIG. 1, and

FIG. 4 shows a schematic diagram of another design of an illuminationarrangement.

In FIG. 1 is shown a section view and a cutout of an optical measuringdevice 10 with a housing 12 wherein the optic is accommodated, which isnot shown, by means of which a radiation reflected by an object to bemeasured is imaged in a camera such as a CCD camera. The optic can beconfigured therein as zoom optic with a variable working distance, whoselens groups can be displaced independently from one other as disclosedin WO 99/53268. This optical measuring device 10 can be in particularpart of a coordinate measuring system.

A support 16 is arranged concentrically with respect to the optical axis14 of the optic, in which light sources, preferably in the form of LEDs,are arranged on circles running concentrically toward each other andradially offset with respect to each other. In the section viewaccording to FIG. 1, the LEDs 18, 20 are arranged on a first circle, theLEDs 22, 24 are arranged on a second circle, the LEDs 26, 28 arearranged on a third circle, the LEDs 30, 32 are arranged on a fourthcircle, and the LEDs 34, 36 are arranged on a fifth circle.

For this purpose, the support 16 has holders 38, 40, 42, 44, and 46arranged on circles running concentrically toward each other for theLEDs 18, 20, 22, 24, 26, 28, 30, 32, 34, and 36, wherein these arearranged in such a way in the holders 38, 40, 42, 44, and 46 thatdifferent incidence angles result with respect to the optical axis 14.In this way, for example, the openings 38 are arranged on a circle onwhich the LEDs enclose an incidence angle α of approx. 70° with respectto the optical axis 14. By means of the openings 40 arranged on acircle, the LEDs are aligned at an angle β of, for example, 35° withrespect to the optical axis 14. Concerning the openings 42 can be presetan angle γ of about 10°. The openings 44 lie again on a circle runningconcentrically with respect to the optical axis so as to intersect theLEDs at an incidence angle δ of, for example, 25°. Regarding theopenings 46 can result, for example, an angle κ of 50°, while thedisclosed values are mentioned purely as examples.

By means of the previously mentioned configuration of the support 16 itis achieved that the LEDs 18, 20, 22, 22, 24, 26, 28, 30, 32, 34, and 36arranged on the circles running concentrically with respect to eachother, which are represented by the holders 38, 40, 42, 44, and 46,intersect the optical axis 14 at different incidence angles inoperational ranges, which are spaced with respect to each other, whichare illuminated along the optical axis 14, and which are designated withthe reference numerals 48, 50, 52, 54, and 56 in FIG. 1.

If, for example, a surface to be measured or an edge of an object islocated within the operational range or within the working plane 52,then the light diodes 26, 28 are used, which illuminate optimally theworking plane 52. If the working distance is changed, for example, bydisplacing the working distance within the plane 54, are then insteadoptimally active the light diodes 30, 32. Thus, it can be optimallymeasured over a large working distance range without requiring amechanical displacement of the LEDs 18, 20, 22, 24, 26, 28, 30, 32, 34,and 36 or the support 16 with respect to the housing 12 thataccommodates the optic.

The light sources are always aligned in such a way with respect to eachother, that their beams meet within a predetermined working plane orilluminate a corresponding working plane. This again means that an areato be measured is always aligned with respect to the correspondingworking plane.

Because in the illumination arrangement of the invention, the LEDs 18,20, 22, 24, 26, 28, 30, 32, 34, are arranged on rings thatconcentrically enclose the optical axis 14 at defined angles indifferent sections of the optical axis 14, these are focused on anotherpoint of the optical axis 14 of the optic, that is, in the exemplarydesign of FIG. 1 they are focused on the intercept points between theoptical axis 14 and the operational ranges or working planes 48, 50, 52,54, and 56. While the focusing of the imaging system, that is, whilefocusing the optic on the corresponding intercept point, is produced adifferent beaming angle between the illumination angle and the surfaceof the object to be measured, so that an optimal illumination andconsequently a high quality measurement is ensured.

As clarified in particular in FIG. 2, the height of the support 16 isrelatively low notwithstanding the possibility that by means of thelight diodes 18, 20, 22, 24, 26, 28, 30, 32, 34, and 36 can be obtainedincidence angles with respect to the axis 14 within the range between 5°and 85° or more, and thus a correspondingly long operational range ismade available, within which measurements can be carried out, so thatthe danger of collisions with an object to be measured are precluded.

For this purpose, it is especially provided that the surface 58 of thesupport 16 on the object side has a curvature radius R especially withina range between 30-90 mm, preferably 50-70 mm. As a consequence of thecurvature radius R, the diameter of the support 16 itself is relativelysmall, whereas the inner diameter amounts to a maximum of 4 to 5 timesthe minimal working distance between the free lower side of the support16 and an object to be measured. Thus, the distance between the lightdiodes 18, 20, 22, 24, 26, 28, 30, 32, 34, and 36 and the object to bemeasured is relatively small, so that again a high lighting is ensured.

While measuring, an object can be moved within the operational range inwhich an optimal illumination takes place. In dependence upon the lightsources used until now can then be automatically adjusted the workingdistance of the measuring optic. There is in contrast the possibility ofadjusting the optic without problem to a specific working distance,wherein the light sources, which are aligned with respect to thisworking distance, are switched on in dependence upon the workingdistance.

Furthermore, in the schematic diagram of FIG. 1 it can be seen thatalong the optical axis 14 can be imaged a bright field incidentradiation by means of optical deflecting elements 58, 60.

The design in FIG. 3 differs from the one in FIG. 1 to the effect thatthe support does not have a hood or calotte-shaped geometry with respectto the arrangement of the light sources 18, 20, 22, 24, 26, 28, 30, 32,34, and 36, but rather a rod or disk-shaped geometry, in which the lightsources 18, 20, 22, 24, 26, 28, 30, 32, 34, and 36 are arranged within aplane, which preferably intersects vertically the optical axis 14.

If the support 16 is preferably basically a dial, which concentricallyencloses the optic, then the light diodes 18, 22, 26, 30, and 34, on theone hand, and 20, 24, 28, 32, and 36, on the other hand, can be arrangedalternatively within the cube or beam-shaped holders, which run parallelto each other.

If in the exemplary design of FIGS. 1 and 2 is provided a support, whichhas the sphere or calotte-shaped geometry with respect to the holders orarrangements of the light sources, then there is also the possibilityaccording to FIG. 4 (as well as according to FIG. 3) of arranging thelight sources 60, 62, 64, 66, and 68 at different incidence angles,which intersect the optical axis in areas, which are spaced with respectto each other. The light sources 60, 62, 64, 66, and 68 can be arrangedin cubical or beam-shaped holders as the support 70, which in turn spana plane that runs especially vertical to the optical axis. A ringarrangement can also be selected, wherein the corresponding support canform a disk. The light sources 60, 63, 64, 66, and 68 can thus bearranged within a mutual plane, which runs parallel to the plane spannedby the support 70. To be able to illuminate the object 72 at differentincidence angles, it is therefore necessary that the support 70 bedisplaced along the optical axis, that is, in accordance with the doublearrow 74. In dependence upon the position of the support 70, lightsources 60, 62, 64, 66, and 68 are activated at different incidenceangles, whereby the object 72 is illuminated at different angles. Thisis clarified purely on principle in view of FIG. 4.

Regardless of this, the arrangement of FIG. 4 obeys the teaching of theinvention insofar as, if the support 70 is fixedly arranged, the axes ofthe light sources 60, 62, 64, 66, and 68 intersect the optical axis inareas, which are spaced with respect to each other.

1. A measuring device, comprising: an illumination arrangement forilluminating an object to be measured comprising several light sources(18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 60, 62, 64, 66, 68) going outfrom a support (16, 70) as well as an optic by means of which the objectcan be measured or imaged, where the light sources are arranged such inthe support (16, 70), that incidence angles (α, β, γ, δ, κ) intersectthe optical axis of the optic in different areas (48, 50, 52, 54, 56),wherein the optic (48, 50, 52, 54, 56) of the measuring device designedas coordinate measuring device is a zoom optic with variable workingdistance, that the incidence angles (α, β, γ, δ, κ) of the light sources(18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 60, 62, 64, 66, 68) arearranged such that incidence angles of light sources intersect theoptical axis (14) in each adjusted working distance regions of theoptic, or that the optic has a constant working distance and the object(72) is illuminable by moving the support (70) along the optical axis(14) relatively to the optic under different angles of incident light.2. The measuring device of claim 1, wherein the light sources (18, 20,22, 24, 26, 28, 30, 32, 34, 36) are arranged on circles concentrically,which enclose the optical axis (14), while the light sources (18, 20,22, 24, 26, 28, 30, 32, 34, 36) arranged on circles of differentdiameters intersect the optical axis (14) in divergent areas (48, 50,52, 54, 56).
 3. The measuring device of claim 1, wherein the lightsources (18, 20, 22, 24, 26, 28, 30, 32, 34, 36), especially LEDs, arearranged on mutually successive circles, which are radially offset withrespect to each other.
 4. The measuring device of claim 1, wherein thesupport (16) encloses the optical axis (14) concentrically and in acollision-free way with respect to the object to be measured.
 5. Themeasuring device of claim 1, wherein the support (16) for the lightsources (18, 20, 22, 24, 26, 28, 30, 32, 34, 36) has a hood orcalotte-shaped geometry with recesses such as bores (38, 40, 42, 44,46), in which the light sources are arranged.
 6. The measuring device ofclaim 1, wherein the support (70) accommodates the light sources (60,62, 64, 66, 68) within a plane that intersects the optical axispreferably vertically.
 7. The measuring device of claim 1, wherein thesupport (72) has a disk-shaped geometry such as a dial-shaped geometry.8. The measuring device of claim 1, wherein the support has a cubic orblock-shaped geometry.
 9. The measuring device of claim 8, wherein thesupport consists of cubic or block-shaped sections running diametricallyto the optical axis (14).
 10. The measuring device of claim 1, whereinthe support (70) is configured so as to be vertically displaceable. 11.The measuring device of claim 1, wherein the support (70) can bedisplaced manually or automatically parallel to the optical axis. 12.The measuring device of claim 1, wherein, if the working distance of theoptic is constant, the object (72) can be illuminated by displacing thesupport (70) along the optical axis (14) at different light incidenceangles.
 13. The measuring device of claim 6, wherein the support (16)has on the side of the object a curvature radius R of 40 mm≦R≦80 mm, inparticular R of about 60 mm.
 14. The measuring device of claim 1,wherein the radiation emitted by the light sources (18, 20, 22, 24, 26,28, 30, 32, 34, 36) is deflected in such a way, that the object can beilluminated in the bright field incident light.
 15. The measuring deviceof claim 1, wherein the light sources (18, 20, 22, 24, 26, 28, 30, 32,34, 36) can be arranged so as to be displaceable within holders (38, 40,42, 44, 46) of the support (16).
 16. The measuring device of claim 1,wherein the light sources (18, 20, 22, 24, 26, 28, 30, 32, 34, 36) arearranged so as to be fixed within the support (16).
 17. The measuringdevice of claim 1, wherein the light sources (18, 20, 22, 24, 26, 28,30, 32, 34, 36) are aligned fiber bundles and/or fiber ring segments.18. The measuring device of claim 1, wherein the light sources (18, 20,22, 24, 26, 28, 30, 32, 34, 36) are radiations reflected by the mirrors.19. The measuring device of claim 1, wherein a bright field incidentradiation can be mirrored along the optical axis (14).
 20. The measuringdevice of claim 1, wherein the light sources (18, 20, 22, 24, 26, 28,30, 32, 34, 36) illuminate the object with divergent colors.
 21. Themeasuring device of claim 1, wherein the light sources (18, 20, 22, 24,26, 28, 30, 32, 34, 36) with the same incidence angles (α, β, γ, δ, κ)illuminate the object with the same color.
 22. A process forilluminating an object with several light sources having differentincidence angles with respect to an optical axis of an optic of ameasuring device, with which the object is measured or imaged, wherein azoom optic with variable working distance is used, and the incidenceangle of the light sources is aligned in such a way with respect to theoptical axis that different light sources intersect the optical axis inareas, which are spaced with respect to each other, wherein if theworking distance of the optic is fixed, the support is displaced alongthe optical axis to illuminate the object at different incidence angles,wherein the light sources, whose incidence angle are aligned toward theworking distance, illuminate the object in dependence upon the workingdistance of the optic.
 23. The process of claim 22, wherein the workingdistance of the optic is adjusted in dependence upon the incidence angleof the light sources that illuminate the object.